The invention relates to a hydraulic control system for an actuator in a vehicle gearbox and also to a method of operating a control system of this kind. Hydraulic control systems of this kind are known from DE 10 2008 016 499 A1.
The invention is described below in connection with a gearbox for a passenger car. However, this should not be regarded as a limitation on the invention. A general goal of automotive engineering is that of increasing efficiency. There is substantial potential for efficiency improvements in the area of secondary consumers. This also includes the hydraulic actuation of clutches and brakes in a vehicle gearbox, in particular in an automatic or automated gearbox.
It is known from the state of the art, in particular from DE 10 2008 016 499 A1, for at least two circuits to be provided to supply a vehicle gearbox, one of which is a high-pressure circuit and the other of which is a low-pressure circuit. The high-pressure circuit is provided to interact with the hydraulic actuators, in particular the clutches and brakes for gear-changing, and the low-pressure circuit is provided to supply lubricating oil and for gearbox cooling.
A problem addressed by the invention is that of specifying a hydraulic control system for a motor vehicle gearbox, wherein the efficiency of this control system is improved.
This and other objects are achieved by a hydraulic control system and also by a method for operating such a hydraulic control system in accordance with embodiments of the invention.
This kind of hydraulic control system for a vehicle gearbox is set up to control the actuating force of at least one hydraulic actuator that can be actuated by a hydraulic medium. The hydraulic actuator, preferably a hydraulic cylinder for exerting an actuating force on the friction linings of a clutch or brake, as these are provided to bring about a gear change in a vehicle gearbox, has at least one oil supply port. Actuators of this kind preferably have an additional return port with which the hydraulic medium can move back in the direction of the hydraulic tank following actuation; more preferably, the oil supply port is also simultaneously configured as a return port. Within the meaning of the invention, a hydraulic medium is preferably taken to mean oil, preferably gear oil.
In order to supply the vehicle gearbox with a hydraulic medium at high pressure, at least one high-pressure hydraulic pump is preferably provided. In this case, within the meaning of this invention, high pressure is taken to mean a hydraulic pressure of 5 bar or more, preferably of 10 bar or more, preferably of 25 bar or more and particularly preferably of 50 bar or more, and further of 300 bar or less, preferably of 175 bar or less, preferably of 100 bar or less and particularly preferably of 75 bar or less. Furthermore, a line for conducting the hydraulic medium at high pressure is preferably referred to as a high-pressure line. The high-pressure line is preferably arranged downstream on the side of a control valve which faces the high-pressure pump. In this case, downstream should, in particular, be taken to mean the direction from one of the hydraulic pumps via the control valve—in this case, this control valve may preferably be set up for pressure regulation—to the hydraulic actuator. A control valve of this kind should preferably be understood to mean a directional valve. Directional valves are known from the state of the art as longitudinal and rotary slide valves. More preferably, a directional valve of this kind is set up to connect different valve ports to one another selectively and preferably to regulate the pressure to which an actuator that can be controlled by the directional valve can be exposed.
In order to supply the vehicle transmission with a hydraulic medium at low pressure, at least one low-pressure hydraulic pump is preferably provided. In this case, within the meaning of this invention, low pressure is taken to mean a hydraulic pressure greater than 0 bar or more, preferably of 1 bar or more, preferably of 5 bar or more and particularly preferably of 7.5 bar or more, and further of 75 bar or less, preferably of 50 bar or less, preferably of 20 bar or less and particularly preferably of 10 bar or less. More preferably, the low-pressure hydraulic pump has a particularly large conveying volume. The volume flow that can be generated using the low-pressure hydraulic pump is preferably greater than the volume flow that can be generated with the high-pressure hydraulic pump, preferably 1.5 times as great or greater, more preferably twice as great or greater, preferably 5 times as great or greater and particularly preferably 10 times as great or greater. Furthermore, a line for conducting the hydraulic medium at low pressure is preferably referred to as a low-pressure line. The low-pressure line is preferably arranged downstream on the side of the control valve facing the low-pressure pump.
Within the meaning of the invention, a hydraulic tank for receiving the hydraulic medium from a return line should be understood to mean a container which is set up to receive and store a hydraulic medium. The hydraulic tank should preferably be understood to mean a hydraulic oil tank and preferably for the oil pump of a gearbox unit.
Within the meaning of the invention, a hydraulic control valve should be understood to mean a directional valve with at least three control positions and at least four valve ports. In the control positions, different valve ports can be selectively connected to one another in a fluid-conducting fashion by valve-internal lines. More preferably, the individual control positions can be achieved by moving a control piston in a valve housing. The control positions can preferably be reached by a longitudinal displacement of the control piston, preferably by a rotation. More preferably, with the control valve in at least one of its control positions, a pressure of the hydraulic medium can be regulated. More preferably, the control valve has at least four valve ports for connecting lines which are set up to conduct the hydraulic medium and at least three control positions, wherein the ports in the control positions can be selectively connected to one another.
According to the invention, in a first control position of the control valve, the high-pressure line can be connected to the oil supply port in a fluid-conducting fashion, in particular to regulate the actuating force of the hydraulic actuator.
More preferably, in a second control position, the low-pressure line can be connected to the oil supply port in a fluid-conducting fashion, in particular for pre-charging the hydraulic actuator. The hydraulic control is preferably provided for controlling at least one and preferably a plurality of hydraulic actuators, in particular of cylinders. Cylinders of this kind, in particular for actuating brakes or clutches, frequently cover a distance initially during actuation, in which practically no or only small amounts of force are to be applied, in particular to overcome play. When this play has been overcome, the hydraulic actuator applies the necessary actuating force. According to the invention, the hydraulic actuator is controlled by low pressure, particularly in order to overcome the play in the second control position of the control valve with the hydraulic medium.
More preferably, in a third control position the hydraulic actuator can be connected to the return line in a fluid-conducting fashion, in particular for the return flow of the hydraulic medium. In particular, a hydraulic control system of this kind makes it possible during actuation of the hydraulic actuator for a dead section of the actuator, in particular the clearance, so in particular the path from the opened position of a clutch or brake to the position where the friction linings are initially brought into abutment, to be quickly overcome by the feeding of the large volume flow from the low-pressure line (first actuation phase). And furthermore (second actuation phase), the hydraulic actuator is thereafter exposed to the high pressure from the high-pressure hydraulic line and the actuating force of the hydraulic actuator can thereby be controlled or regulated as required by the control valve. Through a hydraulic control system of this kind, the degree of effectiveness and therefore the efficiency can be further increased.
In a preferred embodiment, the control valve of the hydraulic control system is configured as a 6/3-way valve and therefore has six valve ports and three control positions. A valve of this kind allows a particularly simple design of the directional valve and therefore a high degree of operational reliability can be achieved.
In a preferred embodiment, the control valve is configured as a 5/3-way valve with five valve ports and three control positions. This 5/3-way valve preferably has two ports downstream on the side facing the hydraulic actuator and three valve ports on the side facing the high-pressure line. One of these three valve ports is preferably connectable to the high-pressure line, one to the low-pressure line and one to the return line. These two valve ports are preferably combined through hydraulic lines, preferably outside the control valve, into a common oil supply port for the hydraulic actuator. More preferably, one of these two valve connections is configured as a return port and the other as an oil supply port. In particular, with a 5/3-way valve as the control valve, it is possible for the control system according to the embodiment to be provided at low structural cost.
In a preferred embodiment, in at least one of the control positions of the control valve, two valve ports are connected downstream on the side of the high-pressure line to two valve ports on the side of the hydraulic actuator in a fluid-conducting fashion. Furthermore, in preferably at least two further control positions, only one of the valve ports is connected downstream on the side of the pressure line in a fluid-conducting fashion to only one of the valve ports on the side of the hydraulic actuator.
In this case, in the context of this invention, connecting valve ports on the two different sides of the control valve should be understood to mean that the valve connections are selectively connected to one another in a fluid-conducting fashion by the different control positions of the control valve. In particular, this kind of control valve as a directional valve makes it possible for a particularly simple and therefore also operationally reliable design of the hydraulic control system to be produced.
In a preferred embodiment, a non-return valve is arranged in at least one connection line downstream between the low-pressure line and the control valve, or else in the low-pressure line. This non-return valve is preferably arranged in such a manner as to prevent the backflow of hydraulic medium from the control valve into the low-pressure line.
In a preferred embodiment, in at least one connection line which is downstream between one of the valve ports and the oil-pressure supply port, a non-return valve is arranged. More preferably, this valve port is arranged in a manner connectable to the low-pressure line in a selectively fuel-conducting fashion and downstream on the side of the valve facing the hydraulic actuator. This non-return valve is preferably arranged in such a manner as to prevent the return flow of hydraulic medium from the control valve into the low-pressure line, i.e., from the oil pressure supply port to the aforementioned valve port.
In particular, when the high-pressure line and the low-pressure line are in fluidic connection to one another, it may be that the hydraulic medium does not reach the hydraulic actuator, but instead is forced into the low-pressure line and the actuating force of the actuator is thereby limited or reduced.
In a preferred embodiment, the control valve is configured as a 4/3-way valve. A control valve of this kind preferably has four valve ports and three control positions. More preferably, the control valve has a valve port downstream on the side facing the hydraulic actuator and three valve ports on the side facing the high-pressure line. In particular, through a valve of this kind a further simplified design of the hydraulic control system is made possible.
In a preferred embodiment, the control valve has three control positions and, furthermore, there is preferably a single valve port in each of these control positions, downstream on the side of the high-pressure line, which can be connected to a single valve port, downstream on the side of the hydraulic actuator. The through-flow through the other valve connections in each case is preferably blocked by the control valve for the hydraulic medium. Through an embodiment of the control valve of this kind, a particularly simple inner structure of the valve can be achieved and a high operational reliability can therefore be achieved.
In a preferred embodiment, the hydraulic actuator is configured as an actuating cylinder for a preferably frictional brake or clutch and, more preferably, a positive switching element with claws or teeth, preferably a claw coupling or sliding sleeve, in a motor vehicle gearbox. What is characteristic of brakes or clutches of this kind is that they are initially adjusted without the actuation cylinder having to apply a substantial actuating force for this purpose; this is particularly the case when it comes to overcoming the play between the friction linings. Particularly when this play is overcome, in other words the friction linings are brought into abutment, the actuating force required for the transmission of forces by the clutch or brake must be applied by the actuating cylinder. According to an embodiment of the invention, in a first movement phase the low-pressure line is connected by the control valve to the oil supply port, and in a second movement phase the high-pressure connection is additionally or alternatively connected to the oil supply port. This embodiment of the invention makes it possible, in particular, to expose the actuating cylinder to hydraulic medium at low pressure initially and then at high pressure, so that an improved hydraulic control system can be achieved.
In a preferred embodiment, the high-pressure and low-pressure hydraulic pumps are preferably configured in a shared housing and, more preferably, as a so-called dual-flow pump. More preferably, two separate hydraulic pumps are present, one of which is provided as a high-pressure pump and the other as a low-pressure pump. More advantageously, pumps of this kind have a shared drive and can be mechanically coupled to one another and, more advantageously, each of the two pumps has its own drive and these are then coupled to one another electronically.
Pumps of this kind are known from the state of the art. More preferably, a dual-flow pump of this kind has a low-pressure and a high-pressure region. In particular a dual-flow hydraulic pump makes a particularly space-saving design possible and an improved hydraulic control system can thereby be achieved.
The hydraulic control system according to an embodiment of the invention can be operated by an operating method which involves at least the following steps for actuation of the hydraulic actuator:                moving the control valve into a control position (second control position) initially for pre-charging the hydraulic actuator, in which the low-pressure line is connected in a fluid-conducting fashion to the oil supply port and thereafter, and        transferring the control valve into a further control position (first control position) for regulating the actuating force for the hydraulic actuator, in which the high-pressure line is at least connected to the oil supply port in a fluid-conducting fashion.        
Particularly through these steps, an efficiency increase is made possible, as the pre-charging of the hydraulic actuator by way of the low-pressure hydraulic medium can be achieved and the actuating force by the high-pressure hydraulic medium.
In a preferred embodiment, the control valve is configured as an electrically actuatable directional valve. In this directional valve, the first control position, in respect of the displacement path of the directional valve for adopting the different control positions, is arranged between the second and the third control position. In order to actuate the control valve, so in particular to change the control position, an electrical current flows through an electrical actuating mechanism of the control valve. An electrical pre-charging current, in particular for actuating the directional valve and for effecting the pre-charging of the hydraulic actuator, preferably flows through this actuating mechanism. More preferably, this pre-charging current is greater than an electrical pressure-regulating current. This pressure-regulating current is, in particular, provided for operating the directional valve and for effecting regulation of the actuating force of the hydraulic actuator. In particular, with a method of this kind, particularly low currents are necessary and the design of the hydraulic control system is thereby simplified.
In a preferred embodiment of the method, the control valve is configured as an electrically actuatable directional valve and the second control position, in respect of a displacement path of the directional valve for adopting the different control positions, is arranged between the first and the third control position. More preferably, the electrical pre-charging current for actuating the directional valve and for effecting the pre-charging of the hydraulic actuator is smaller than the electrical pressure-regulating current, for actuating the directional valve and for effecting regulation of the actuating force of the hydraulic actuator. In particular, due to an arrangement of the hydraulic control system of this kind and of the method for the operation thereof, a particularly robust regulation of the hydraulic actuator is made possible.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.